1. Field of the Invention
The present invention relates to a method of liquid-cooling an inverter device with a liquid-cooling mechanism in a control box which controls the rotational speed of a pump or the like with the inverter device.
2. Description of the Prior Art
FIGS. 1A and 1B of the accompanying drawings show a conventional control box for controlling the rotational speed of a pump with an inverter device. As shown in FIGS. 1A and 1B, the control box has an inverter device 1, a protective device 5, such as a ground fault interrupter, and a control device 6, such as auxiliary relays which are housed in a console case 3 mounted on a console chassis 4.
The console chassis 4 has a plurality of holes 8 defined therein for passage of electric power cables therethrough. A heat sink 12 is mounted on an outer surface of the console chassis 4. The inverter device 1, which is a heat source, is mechanically coupled to the heat sink 12 that radiates the heat generated by the inverter device 1 through fins of the heat sink 12 into the atmosphere. Therefore, the inverter device 1 housed in the console case 3 is air-cooled through the heat sink 12.
As the output power of the air-cooled inverter device 1 becomes higher, the inverter device 1 radiates a larger amount of heat and requires the heat sink 12 to be larger in size. Since the inverter device 1 is actually relatively small in size, the installation area in which the inverter device 1 is attached to the heat sink 12 is small as compared to the output power of the inverter device 1, as can be seen from the proportion of the size of the inverter device 1 to the size of the heat sink 12 in FIGS. 1A and 1B.
With the size proportion shown in FIGS. 1A and 1B, the heat generated by the inverter device 1 cannot uniformly be transferred to the entire surface of the heat sink 12, and hence cannot sufficiently be dissipated from the heat sink 12, resulting in an undue increase in the temperature of the inverter device 1.
For fully dissipating the heat produced by an inverter device, the inverter device may be water-cooled by a water-cooling heat sink. FIGS. 2A and 2B of the accompanying drawings show a control box having a water-cooling heat sink 2. The control box shown in FIGS. 2A and 2B is essentially similar to the control box shown in FIGS. 1A and 1B except for the water-cooling heat sink 2 which is mounted on an outer surface of the console chassis 4.
The heat generated by the inverter device 1 is radiated into the atmosphere through cooling water which flows in the water-cooling heat sink 2. Specifically, the water-cooling heat sink 2 has a cooling pipe 21 disposed therein and having an inlet port 22 and an outlet port 23. The cooling water is introduced through the inlet port 22 into the cooling pipe 21 and discharged from the cooling pipe 21 through the outlet port 23. A protective device 5 and a control device 6 are also housed in a console case 3.
The water-cooling heat sink 2 is smaller in size than the air-cooling heat sink 12 shown in FIGS. 1A and 1B. However, the relatively small water-cooling heat sink 2 is capable of sufficiently discharging the heat from the inverter device 1 into the atmosphere around the control box.
If the temperature of the water-cooling heat sink 2 is lower than the temperature of air in the control box or the temperature of the atmospheric air, then the moisture present in and around the control box is condensed into dew that tends to corrode the console chassis 4 and also adversely affects the electric components in the control box. If the water-cooling heat sink 2 is directly installed on the console chassis 4, then the heat of the water-cooling heat sink 2 is transferred to the console chassis 4. Therefore, when the temperature of the water-cooling heat sink 2 is lower than the temperature of air in the control box or the temperature of the atmospheric air, the moisture present in and around the control box is condensed into dew on the inner and outer surfaces of the control chassis 4.
FIGS. 3A and 3B of the accompanying drawings show control box structures for preventing moisture condensation on a control box chassis. In FIG. 3A, a water-cooling heat sink 2 is spaced from a console chassis 4 by a spacer 9 and connected to the console chassis 4 by a bolt 7 spaced from the spacer 9. In FIG. 3B, a water-cooling heat sink 2 is spaced from a console chassis 4 by a spacer 9 and connected to the console chassis 4 by a bolt 7 extending through the spacer 9. In each of the structures shown in FIGS. 3A and 3B, a heat source, such as an inverter device, is connected to the water-cooling heat sink 2 to transmit the heat generated by the heat source to the water-cooling heat sink 2, which transfers the heat out of the control box. Since the water-cooling heat sink 2 is positioned outside of the control box with a space left between the console chassis 4 and the water-cooling heat sink 2, the heat of the water-cooling heat sink 2 is essentially not transferred to the console chassis 4. As a result, no moisture condensation takes place on the inner and outer surfaces of the console chassis 4. Even when moisture is condensed on the water-cooling heat sink 2, the condensed water does not find its way into the control box.
However, the structures shown in FIGS. 3A and 3B are not addressed to the problem of how to remove dew produced upon moisture condensation on the surface of the water-cooling heat sink 2 and also the problem of moisture condensation on the inverter device mounted on the water-cooling heat sink 2 and connecting portions of wires and cables connected to the inverter device.
The mechanical structure of a general inverter device which is housed in a control box is shown in FIGS. 4A and 4B of the accompanying drawings. As shown in FIGS. 4A and 4B, the inverter device has a frame assembly comprising a resin frame 113 extending around a copper plate 115. The frame assembly supports a base board 114 encapsulated by a resin mold 116. The base board 114 supports thereon various electronic components required to control the inverter device and power semiconductor devices for the inverter device. Those electronic components include a control power supply capacitor 110, a control power supply transformer 111, and a control CPU 112 which are mounted on the base board 114 and wholly or partly exposed for heat radiation. Power supply terminals 120 are also exposed on the base board 114. The inverter device also includes an intermediate voltage board 117 supporting capacitors 119. The intermediate voltage board 117 is fastened to the base board 114 by screws 118.
FIG. 5 of the accompanying drawings shows the control power supply capacitor 110 which is mounted on the base board 114. As shown in FIG. 5, capacitor attachment terminals 121 connected to the control power supply capacitor 110 are attached to the base board 114 and partly encapsulated by the resin mold 116. Inasmuch as the capacitor attachment terminals 121 cannot be fully encapsulated by the resin mold 116 in order to radiate the heat from the control power supply capacitor 110, upper portions of the capacitor attachment terminals 121 are exposed.
FIG. 6 of the accompanying drawings illustrates the control CPU 112 which is mounted on the base board 114. As shown in FIG. 6, the control CPU 112 is partly encapsulated by the resin mold 116. The control CPU 112 has control CPU terminals 125 connected to the base board 114. Since the control CPU 112 generates heat, it is fully covered with a copper plate 115 for heat radiation.
FIGS. 7A and 7B of the accompanying drawings show the power supply terminals 120 in detail. As shown in FIGS. 7A and 7B, a terminal attachment bar 124 is directly mounted on the base board 114 and has a plurality of screw holes defined in an upper surface thereof. The power supply terminals 120, which are of the pressure type, are attached to the terminal attachment bar 124 by respective screws 123 that are threaded into the respective screw holes. The terminal attachment bar 124 has partition walls 122, and integrally molded with the resin frame 113 for separating the power supply terminals 120 from each other. Power supply wires 126 are connected to the respective power supply terminals 120.
When the temperature of the cooling water supplied to the water-cooling heat sink is low, the temperature of the copper plate 115 shown in FIG. 4 is close to the temperature of the surface of the heat sink, i.e., the temperature of the cooling water flowing through the heat sink. Since the resin mold 116 is cooled to the temperature of the copper plate 115, the temperature of the base board 114 is also close to the temperature of the cooling water. The control power supply capacitor 110 is cooled to an overly cooled condition through the capacitor attachment terminals 121 which are connected to the base board 114. Similarly, as shown in FIG. 6, the control CPU 112 is cooled to an overly cooled condition through the control CPU terminals 125 which are connected to the base board 114. Moreover, as shown in FIGS. 7A and 7B, the power supply terminals 120 are cooled to an overly cooled condition through the screws 123 and the terminal attachment bar 124 which is connected to the base board 114.
As described above, when the temperature of the cooling water supplied to the water-cooling heat sink is low, the cooling water has its cooling effect on the various electronic components of the inverter device. As a result, the various electronic components are cooled. If the surface temperature of the various electronic components or wires connected thereto becomes lower than the dew point, then moisture is condensed on and around the electronic components, tending to impair the insulating capability thereof or produce a short circuit between the electronic components or in the power supply system. Such an insulation failure or short circuit may possibly lead to a serious accident.
Specifically, in FIG. 5, the moisture is condensed on and around the control power supply capacitor 110, producing dew which drops onto the capacitor attachment terminals 121 thereby to cause a short circuit between the capacitor attachment terminals 121.
In FIG. 6, the moisture is condensed on and around the heat-radiating copper plate of the control CPU 112, producing dew which drops onto and spreads over the resin mold 116. The spread dew causes a short circuit between pins of nearby connectors, which results in a malfunction of the control CPU 112.
In FIGS. 7A and 7B, the moisture is condensed on and around the screws 123 and the terminal attachment bar 124, producing dew which is gathered on the partition walls 122 thereby to bring about a short circuit in the power supply system. Because the wires 126 connected to the power supply terminals 120 are heat conductors, the wires 126 themselves are cooled, resulting in a degradation of the insulation of the wires 126.
If part of a liquid that is delivered under pressure by the pump whose rotational speed is controlled by the inverter device is used as the cooling water, then it is difficult to control the temperature of the cooling water because the pump can handle a wide range of alternative liquids which have a wide temperature range. Unless the temperature of the cooling water is strictly controlled, however, the inverter device may possibly suffer a serious accident due to moisture condensation as described above. For example, if the pump handles tapped water, then it has different temperatures in summer and winter. If the pump handles groundwater, then its temperature is very low even in summer, and it is likely to overly cool the inverter device.
In reality, therefore, almost all inverter devices used for the control of general pumps are air-cooled either through radiation or by a fan.
As described above, the water-cooling heat sink can reliably discharge the heat generated by the power semiconductor devices, but may possibly overly cool the electronic components and/or conductors or wires connected thereto. Therefore, the water-cooling heat sink requires that the temperature of the cooling water be controlled so as not cause moisture condensation, and be determined in view of the ambient temperature and/or humidity. While the temperature of the cooling water can be controlled if the cooling water is supplied from an external source, it is almost impossible to control temperature of the cooling water if it is part of a liquid that is handled by the pump controlled by the inverter device itself.
FIG. 8 of the accompanying drawings shows a liquid-cooling mechanism for cooling an inverter device with a liquid which is handled by a pump whose rotational speed is controlled by the inverter device. As shown in FIG. 8, a pump 8 has an outlet port which is connected to a check valve 81. Part of a liquid that is discharged by the pump 8 is introduced from between the outlet port and a primary side of the check valve 81 through a conduit 82 to an inlet port 22 of a pipe 21 which extends through a heat sink 2. The liquid which flows through the pipe 21 is then discharged from the water-cooling heat sink 2 through an outlet port 23 of the pipe 21, and returns through a return pipe 84 to a short pipe 83 which is connected to a suction port of the pump 8.